Steam turbomachine having a bypass circuit for throttle flow capacity adjustment

ABSTRACT

A steam turbomachine includes a housing having a shell that defines a steam flow path, a first stage bowl cavity formed in the shell, a first stage including a plurality of first stage nozzles and a plurality of first stage buckets arranged downstream of the plurality of first stage nozzles, a second stage including a plurality of second stage nozzles and a plurality of second stage buckets arranged downstream of the plurality of second stage nozzles. The second stage is arranged downstream of the first stage along the steam flow path. A bypass circuit is formed in the shell. The bypass circuit extends from a first end fluidically connected to the first stage bowl cavity to a second end fluidically exposed to the steam flow path upstream of the second stage. A valve element is positioned in, and selectively blocks, the bypass circuit.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to the art of steam turbomachines and, more particularly, to a steam turbomachine having a bypass circuit for throttle flow capacity adjustment.

In a steam turbomachine, high pressure, high temperature steam is utilized as a working fluid. Inlet steam is passed through a plurality of nozzles toward a plurality of buckets coupled to a shaft. The nozzles redirect and accelerate the inlet steam which then flows onto the buckets. Upon contact with the high temperature, high pressure steam, the buckets rotate thereby transforming thermal energy from the steam to mechanical, rotational, energy that drives the shaft. The shaft is employed to drive a component such as a generator or a pump.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the exemplary embodiment, a steam turbomachine includes a housing having a shell that defines a steam flow path, a first stage bowl cavity formed in the shell, a first stage including a plurality of first stage nozzles and a plurality of first stage buckets arranged downstream of the plurality of first stage nozzles, a second stage including a plurality of second stage nozzles and a plurality of second stage buckets arranged downstream of the plurality of second stage nozzles. The second stage is arranged downstream of the first stage along the steam flow path. A bypass circuit is formed in the shell. The bypass circuit extends from a first end fluidically connected to the first stage bowl cavity to a second end fluidically exposed to the steam flow path upstream of the second stage. A valve element is positioned, in and selectively blocks, the bypass circuit.

According to another aspect of the invention, a method of adjusting throttle flow capacity in a steam turbomachine includes guiding steam along a steam flow path of the steam turbomachine, the steam passing through a first stage and a second stage, and delivering an amount of steam from the first stage bowl to the steam flow path upstream of the second stage bypassing the first stage.

These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF DRAWINGS

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a partial cross-sectional schematic view of a steam turbomachine having a bypass circuit and valve element access passage in accordance with an exemplary embodiment;

FIG. 2 is a partial cross-sectional view of the steam turbomachine of FIG. 1 illustrating the valve element in a partial bypass position; and

FIG. 3 is a partial cross-sectional view of the steam turbomachine of FIG. 2 illustrating a locking member abutting the valve element.

The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

A steam turbomachine in accordance with an exemplary embodiment is indicated generally at 2 in FIG. 1. Steam turbomachine 2 includes a housing 4 having an outer shell 6 and an inner shell 8 including a first inner shell half 10 joined to a second inner shell half (not shown) along a horizontal joint (also not shown). Of course it should be understood that turbomachine 2 may include only a single shell. Inner shell 8 defines, at least in part, a steam flow path 12 along which extend a plurality of stages 16. In the embodiment shown, plurality of stages 16 includes a first stage 20, a second stage 22 and a third stage 24. It should however be understood that the number of stages may vary. First stage 20 includes a plurality of first stage nozzles 30 arranged upstream from a plurality of first stage buckets 33. First stage nozzles 30 are supported to inner shell 8 by a nozzle plate assembly such as shown at 34 and first stage buckets 33 are connected to a rotor shaft 35.

Similarly, second stage 22 includes a plurality of second stage nozzles 36 arranged upstream of a plurality of second stage buckets 38. Second stage nozzles 36 are supported to inner shell 8 through a nozzle diaphragm assembly 39 and second stage buckets 38 are coupled to rotor shaft 35. Third stage 24 includes a plurality of third stage nozzles 40 arranged upstream of a plurality of third stage buckets 42. Third stage nozzles 40 are supported to inner shell 8 through a nozzle diaphragm assembly 43 and third stage buckets 42 are coupled to rotor shaft 35. Steam turbomachine 2 is also shown to include a first stage bowl cavity 44 arranged upstream of first stage 20.

High temperature, high pressure steam is introduced into first stage bowl cavity 44 and passed through a bowl annulus 45 to steam flow path 12. The high pressure, high temperature steam expands through plurality of stages 16 along steam flow path 12. The high temperature, high pressure steam initially passes through first stage nozzles 30 which impart a desired flow angle and exit velocity. The high temperature, high pressure gases impact the plurality of first stage buckets 33 at the desired flow angle imparting a rotation force to a first stage wheel (not separately labeled). The high temperature, high pressure gases flow to second stage 22, passing through the plurality of second stage nozzles 36 and acting upon second stage buckets 38, and third stage 24, passing through the plurality of third stage nozzles 40 and acting upon third stage buckets 42. Plurality of stages 16 transforms thermal energy from the high temperature, high pressure gases into mechanical, rotational energy, to rotor shaft 35 that may be used to drive a mechanical device such as a generator, a pump, or the like.

Manufacturers design steam turbines to possess a predetermined throttle flow capacity which may be dictated by a plant customer. However, computer design models of a steam turbine may differ slightly from an actual steam turbine in operation due to manufacturing tolerances, variations in stage flow characteristics, differences in steam supply, and the like. In such cases, the customer may be disappointed in an actual throttle flow capacity of the steam turbine. In accordance with the present invention, as-built throttle flow capacity of steam turbomachine 2 is selectively adjustable after installation without the need to replace or rebuild portions of steam flow path 12 or stages 16 and without the need to disassemble outer shell 6 to more accurately meet customer requirements, as will be detailed more fully below.

In accordance with an exemplary embodiment, steam turbomachine 2 includes a bypass circuit 50 that extends through inner shell 8. Bypass circuit 50 may be formed entirely within first inner shell half 10, as will be detailed below, or along the horizontal joint by machining mirror image channels (not shown) on both first inner shell half 10 and a second inner shell half (also not shown). Bypass circuit 50 extends from a first end 54 fluidically exposed to first stage bowl cavity 44 to a second end 55 through an intermediate portion 56. Second end 55 is fluidically exposed to steam flow path 12, as will be detailed more fully below. In accordance with one aspect of the exemplary embodiment, second end 55 is fluidically exposed to steam flow path 12 upstream of second stage 22. More specifically, second end 55 is fluidically exposed to steam flow path 12 upstream of the plurality of second stage nozzles 36. It should however be understood that the particular location of second end 55 may vary depending upon how much additional throttle steam flow is desired, which will also depend on flow resistance of bypass circuit 50. In accordance with an exemplary embodiment, steam is bypassed to second stage 22 in order to lessen a reduction in steam path efficiency that may take place. Bypass flow will be constrained by the available pressure drop across, and physical characteristics (cross sectional area and length) of, the bypass circuit 50. Additional bypass flow, if required, may be obtained by bypassing more than one stage at the expense of increased reduction in steam path efficiency.

In accordance with one aspect of the exemplary embodiment, a first inner shell half 10 includes a recess 58 formed downstream of second end 55. In addition, diaphragm assembly 39 includes a plurality of circumferential bypass grooves, one of which is indicated at 60. Bypass grooves 60 extend across an upstream surface of diaphragm assembly 39 and fluidically connect recess 58 with steam flow path 12. More specifically, bypass grooves 60 extend from a first end portion 61 to a second end portion 62 through an intermediate portion 63. First end portion 61 receives steam from first stage bowl cavity 44 via bypass circuit 50, and second end portion 62 delivers bypass steam to steam flow path 12 upstream of second stage nozzles 36.

In still further accordance with the exemplary embodiment, steam turbomachine 2 includes a valve element access passage 80 that bisects bypass circuit 50. Valve element access passage 80 includes a first passage portion 84 that extends through outer shell 6, a second passage portion 85 that extends through inner shell 8, and a recess portion 87. Second passage portion 85 includes a threaded region 89. A valve element 94 is selectively arranged in valve element access passage 80 to adjust a cross-sectional area of bypass circuit 50. Valve element 94 includes a plug body 97 that may have a threaded portion 99 and a non-threaded portion 103.

Threaded portion 99 inter-engages with threaded region 89 to adjust a radial position of valve element 94 in valve element access passage 80. Non-threaded portion 103 may extend into bypass circuit 50. In a fully seated position, in which valve element 94 completely blocks bypass circuit 50, non-threaded portion 103 may nest within recessed portion 87, as shown in FIG. 1. Valve element 94 may be adjusted from the fully seated position to a partial bypass position, as shown in FIG. 2. In either case, a locking member 109 (FIG. 3) may be installed in valve element access passage 80 to prevent movement of valve element 94 during operation of steam turbomachine 2. Both valve element 94 and locking member 109 may include a tool engaging element such as shown at 112 and 114 respectively. Tool engaging elements 112 and 114 provide structure that engages with a setting tool, such as a T-handle wrench 116, to set the desired position of valve element 94 and locking member 109.

At this point it should be understood that the exemplary embodiments provide a system for introducing bypass steam from the first stage bowl cavity into the steam flow path bypassing the first stage of the steam turbomachine. The amount of bypass steam flowing through the bypass circuit may be varied in order to selectively adjust throttle flow capacity of the steam turbomachine. The valve element may be selectively positioned to provide the desired amount of bypass steam. The term “valve element” should be understood to encompass the form shown, as well as other valve-like arrangements such as a ball/barrel valve, a butterfly valve, a needle valve and the like, that provide selective adjustment of steam flow.

Regardless of construction, when the valve element is fully retracted, there will be maximum bypass flow, thus a maximum increase in throttle flow through the turbine. The cross-sectional area of the connecting passageway will dictate the percentage increase in flow when the bypass valve is fully open. The valve element in accordance with the exemplary embodiment allows the throttle flow capacity of the steam turbomachine turbine to be adjusted in the field to a small degree (on the order of a few percent of the valve wide open (VWO) design flow). The bypass may be manually adjustable from outside of the turbine via an access port. The bypass circuit removes steam from the first stage bowl and sends it to a downstream stage bowl. This bypass has the effect of increasing the total flow to the turbine with a minor compromise to steam path efficiency.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims. 

What is claimed is:
 1. A steam turbomachine comprising: a housing having a shell that defines a steam flow path; a first stage bowl cavity formed in the shell; a first stage including a plurality of first stage nozzles and a plurality of first stage buckets arranged downstream of the plurality of first stage nozzles; a second stage including a plurality of second stage nozzles and a plurality of second stage buckets arranged downstream of the plurality of second stage nozzles, the second stage being arranged downstream of the first stage along the steam flow path; a bypass circuit formed in the shell, the bypass circuit extending from a first end fluidically connected to the first stage bowl cavity to a second end fluidically exposed to the steam flow path upstream of the second stage; and a valve element positioned in and selectively blocking the bypass circuit.
 2. The steam turbomachine according to claim 1, further comprising: a valve element access passage extending through the shell, the valve element access passage being fluidically connected to the bypass circuit.
 3. The steam turbomachine according to claim 2, wherein the shell includes an inner shell and an outer shell, wherein the valve element access passage includes a first passage portion extending through the inner shell and a second passage portion extending through the outer shell, the first passage portion being aligned with the second passage portion.
 4. The steam turbomachine according to claim 2, wherein the valve element access passage includes a threaded region configured and disposed to engage with the valve element.
 5. The steam turbomachine according to claim 4, wherein the valve element includes a threaded portion configured to engage with the threaded region.
 6. The steam turbomachine according to claim 5, wherein the valve element includes a non-threaded portion extending from the threaded portion, the non-threaded portion extending into the bypass circuit.
 7. The steam turbomachine according to claim 2, further comprising: a locking member arranged in the valve element access passage outboard of the valve element, the locking member preventing inadvertent removal of the valve element from the valve element access passage.
 8. The steam turbomachine according to claim 1, further comprising: a recess formed in the shell and fluidically connected with the bypass circuit, the recess extending annularly about the housing.
 9. The steam turbomachine according to claim 8, further comprising: one or more bypass grooves extending from the recess to the steam flow path.
 10. The steam turbomachine according to claim 9, further comprising a nozzle diaphragm assembly connected with one of the plurality of second stage nozzles, each of the one or more bypass grooves extending across the nozzle diaphragm assembly.
 11. The steam turbomachine according to claim 10, wherein the one or more bypass grooves are formed on an upstream surface of the nozzle diaphragm assembly.
 12. The steam turbomachine according to claim 1, wherein the second end of the bypass circuit is fluidically exposed to the steam flow path upstream of the plurality of second stage nozzles.
 13. A method of adjusting throttle capacity in a steam turbomachine, the method comprising: guiding steam along a steam flow path of the steam turbomachine, the steam passing through at least a first stage and a second stage; and delivering an amount of steam from a first stage bowl cavity to the steam flow path upstream of the second stage bypassing the first stage.
 14. The method of claim 13, wherein delivering the amount of steam includes selectively guiding steam through a bypass circuit that fluidically connects the first stage bowl cavity and the stem flow path upstream of the second stage.
 15. The method of claim 14, wherein selectively guiding steam through the bypass circuit includes selectively adjusting a cross-sectional area of the bypass circuit.
 16. The method of claim 15, wherein selectively adjusting the cross sectional area of the bypass circuit includes selectively positioning a valve element along a valve element access passage that bisects the bypass circuit.
 17. The method of claim 16, wherein selectively positioning the valve element includes one of threading the valve element into the valve element access passage and threading the valve element out of the valve element access passage.
 18. The method of claim 16, wherein selectively positioning the valve element includes removing the valve element from the bypass circuit.
 19. The method of claim 16, wherein selectively positioning the valve element includes removing the valve element from the valve element access passage.
 20. The method of claim 16, further comprising: installing a locking member in the valve element access passage to prevent movement of the valve element. 